NASA World Wind
This is great! Thanks to Steve Makofsky for pointing it out.
Check out NASA's WorldWind software (it's a free download).
In a nutshell, it allows you to zoom from any satellite altitude into any place on earth using various images captured from LandSat and STRM (Shuttle Radar Topography Mission) elevation data. It's pretty impressive and definitely worth the 231MB download (although, it requires some pretty beefy processing and video power).
More on WorldWind's features can be found here.
Pretty cool that it's written in .NET.